as long as the player playing the game is above the legal aga I think it's OK. Though, I did play violent games such as CS before I was above the legal age.. But my parents made sure that when I got mad because of the game that I would quit for a few days and then try again. IMO, it's quite OK as long as the parents pay attention to the behavior of the kid playing it..
EDIT:
BTW, you guys havent learned anything in school? -.- when you give your meaning, you should also give arguements and examples. You guys are just like: 'Owh, it's ok', 'owh violent games rule' bla bla. It's a fucking disscusion thread, there's nothing to discus as long as you guys don't say anthing more then 5 words.